HOUSTON — The shooter in an apparent murder-suicide at the Johnson Space Center had received a poor job review and feared being fired, police said Saturday.

William Phillips, 60, smuggled a snub-nosed revolver into the space center Friday, shot David Beverly, 62, and barricaded himself with a hostage before shooting himself in a building that houses communications and tracking systems for the space shuttle, officials said.

Houston Police Chief Harold Hurtt said Phillips bought the .38-caliber revolver March 18, two days after receiving an e-mail citing deficiencies in his job performance and saying that he was going to be reviewed.

A copy of the e-mail was found in Phillips’ lunch bag on the day of the shootings, police Lt. Larry Baimbridge said.